Unfortunately, Windows 98 support ended in July of 2006 - http://support.microsoft.com/lifecycle/?p1=6898
At this point the only thing I would use Windows 98 for would be a machine that never attaches to the Internet and is only used to run some "ancient" standalone software that could not be upgraded. It just is not a secure OS at this point.
If you must still use Windows 98, and are in need of a security package for it, look at www.avast.com for a free solution.
-steve